Paul A. Samuelson in his classical article divided goods in general into two categories: \textbf{private consumption goods} $(X_1,...,X_n)$ which can be distributed among individuals and \textbf{collective consumption goods} $(X_{n+1},...,X_{n+m})$ \textit{which all enjoy in common in the sense that each individual's consumption of such a good leads to no subtractions from any other individual's consumption of that good.}\cite{samuelson54}
%\footcite{samuelson54}

\textit{non-rivalrous}

\textit{non-excludable}

